Strong Root System Enhances Waterlogging Resilience in Barley (Hordeum vulgare) at the Early Stage Stress

Barley (<i>Hordeum vulgare</i> L.) is resistant to salt, drought and low temperature stress but sensitive to waterlogging stress. For now, little is known in waterlogging stress about the molecular mechanisms underlying the regulation of hormonal pathways in barley roots. In this study, the effects of waterlogging stress on 33 genotypes during the whole growth stages were comprehensively assessed. Then, the root morphology, hormone content and relative root development gene expressions were investigated in the most waterlogging-sensitive and -tolerant genotypes. We found waterlogging-tolerant genotypes (four representative genotypes) increased root length, forks, surface and project area traits at the early stage of waterlogging stress; meanwhile, these root traits were reduced in waterlogging-sensitive genotypes (four representative genotypes) because of ABA and ethylene inhibition. Furthermore, waterlogging-tolerant barley genotypes, respectively, induced and inhibited the positive (<i>TCP20</i> and <i>PLT2</i>) and negative (<i>SHY2</i> and <i>PILS2</i>) regulated gene's expressions that controlled the meristem growth at the root tips to cope with waterlogging stress. In addition, our results were consistent with the hypothesis that waterlogging-tolerant barley genotypes can simultaneously upregulate GA levels and downregulate ethylene accumulation, which may induce the expression of <i>SHR</i> and <i>SCR</i> genes and enhance root growth under waterlogging stress. This research lays a foundation for the subsequent screening and breeding of waterlogging-tolerant genotypes and the exploration of waterlogging-tolerant mechanisms in barley.